King's English Variation, Three Knights System

After 1. c4 e5 2. Nc3 Nc6, White chooses 3. Nf3 instead of the fianchetto with 3. g3, which leads to the Closed System and related lines. The knight develops toward the center, attacks the e5-pawn and supports a later d4, so Black has to decide at once how to deal with the pressure on e5. The position is classified as ECO A27, and three knights are now in play.

The most common reply by a wide margin is 3...Nf6. It brings out the fourth knight and enters the Four Knights Variation (A28), the main branch of the system. 3...Bc5 is the next most frequent choice. It develops the bishop actively toward f2 and leaves the f-pawn and the knight on g8 flexible. 3...d6 instead covers e5 with a pawn and leads to a more restrained structure. The engine considers the position roughly balanced and prefers 3...Nf6, 3...g6 and 3...Nge7, the last two pointing to fianchetto or Botvinnik-style setups for Black. In practice White scores somewhat better, and draws are rare.